Stuart Twin Victoria (Princess Royal) Mill Engine

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 12/04/2021 06:57:17:

I don't round mine.

Yes once you are close give it a lick with the diamond so it's good and sharp for the last couple of cuts.

Ok thanks.

[Ramon WilsonParticipant @ramonwilson3]

Hi Doc , been out of it for a few days (plastic distraction) so only just caught up with your progress. Nice work on the boring bar and you initial tool grinding. You might find a holder made from round bar more beneficial in creating angles but those you've got so far look just fine. I would use the sharp tip as per the last image for getting under the skin but for a really good finish 'off the tool' on the last ten thou or so I'd grind (not file) a nice radius on that corner.

Keep the speed and feed well down for best results.

Looking good – go for it

Ramon

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ramon Wilson on 12/04/2021 20:48:11:

Hi Doc , been out of it for a few days (plastic distraction) so only just caught up with your progress. Nice work on the boring bar and you initial tool grinding. You might find a holder made from round bar more beneficial in creating angles but those you've got so far look just fine. I would use the sharp tip as per the last image for getting under the skin but for a really good finish 'off the tool' on the last ten thou or so I'd grind (not file) a nice radius on that corner.

Keep the speed and feed well down for best results.

Looking good – go for it

Ramon

Thanks Ramon. I’ve taken a week off work for gardening and changing the rear brakes on the car. Unfortunately the easiest way to change inboard brake callipers is to remove the entire IRS. Got it removed today with the boy helping, next up is swapping the pots and re-fitting without getting squashed.

After that’s done, it’ll be full steam ahead on the P.R., although I’m still battling with an Airfix Swordfish. Shame they decided to put a massive pocket under the upper wing, that results in some subtle but very difficult to remove sink marks. It’s already been in caustic soda once…

Edited By Dr_GMJN on 12/04/2021 22:15:04

[Dr_GMJNParticipant @dr_gmjn]

So it’s the one year anniversary of starting the 10V, so I made a start on this one. This time with some help from my son:

We got the castings and bed material out – shows how much work this is going to be:

After re-figuring out how all the 3D printed jigs were supposed to work, fist job was to trim the bed plate sides to length on the mill:

Small start, but it’s a start.

Next job is to co-ordinate drill the counterbored holes.

[JasonBModerator @jasonb]

Good to see this one underway.

[Dominic BramleyParticipant @dominicbramley60728]

+1 : I've been looking forward to seeing this build

[Dr_GMJNParticipant @dr_gmjn]

Thanks both.

Got the holes drilled and counterbored tonight; they all match – so far.

Very easy to get them mixed up, I’ll have to keep the markings clear to prevent a time consuming mistake.

Still have to drill sockets for the linkage bosses in the inner walls (B & C), then we will see if the 3D printed casting draft jigs work…

[Dr_GMJNParticipant @dr_gmjn]

Decided to get on with the bed cross-pieces and ends. First job: saw 8x blocks a bit oversized, and de-burr:

Then machine to the right width with the shell mill. This wasn’t as easy as it seemed for some reason, and took several goes to get the corners 90 degrees according to the engineer’s square:

I’d machined an end stop for the vice during my dormant modelling phase, and this came in handy as a fixture for the 32 drilled and tapped holes:

Because of the way I’d designed the ends to allow for tapered outer faces, the holes aren’t on the central axis of the end pieces, they are offset inwards slightly. This tripped me up on the first piece, which gave a staggered end:

another lesson learned. I JB Welded some aluminium rod into the holes, faced off and re-drilled. It’s spot-on now.

Then the middle spacers were drilled and tapped, and reduced in height by 5.4mm:

Made another error by drilling the first hole M4 as per the ends, should be M3 to accommodate the taper. Silly error, especially when using my own design/drawings. Anyway, as with the ends, I realised after the first one, and that’ll be corrected by tomorrow. So here we are now:

Next job is to disassemble again, and drill a couple of blind holes in the inner sides for the bosses for the throttle bell cranks, then it’ll be machining the tapers on all the components.

[Dr_GMJNParticipant @dr_gmjn]

So this evening’s job was machining the middle bed spacers to thickness:

Then machining on the simulated casting draw taper. This was a good opportunity for the boy to apply the trigonometry He’s only just done in maths at school. No problem at all – measured the hypotenuse:

And worked out the depth of spacer needed to tilt the vice at 1.5 degrees. Good example of using trig, good timing too.

So we found some scrap, raised the vice and cut the first sides:

Then came the confusion. My assumption was that to get a symmetrical 3 degree taper on the blocks, all we had to do was machine 1.5 degrees on one face, flip it in the vice and machine the other face. I’d assumed that the 1.5 degree face would add to the 1.5 degree vice tilt, giving an overall 3 degrees. When I told him to do this he was having none of it; said it would either give zero degrees, or an asymmetric taper, and that we needed a 3 degree tilt for the second cut. Somewhat taken aback, I decided to prove my point with 2D CAD. Turns out he was right I think.

So we put one of the 3D printed 3 degree wedges I’d made for the long sides under the vice:

And cut the faces:

And they turned out spot-on:

They just need rounds filing on the top edges.

So I suppose the moral is, don’t assume your student necessarily knows less than you.

[JasonBModerator @jasonb]

You are both making good progress, just watch those hoodie strings around machines.

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 14/05/2021 07:04:52:

You are both making good progress, just watch those hoodie strings around machines.

Thanks Jason – very good point about the strings. I should have noticed that before now.

[Dr_GMJNParticipant @dr_gmjn]

Finally got around to using the 3D printed taper jigs today. Set up parallel with the bed, and checked both workpiece positions (they are too long to do in one pass):

Marked out the extents of the taper, and carefully made the first cuts:

un u

All seemed fine, so swapped positions and machines the other end to the same DRO z setting:

With the first pair complete, removed the jigs and replaced with those for the opposite hand, and repeated the process:

The time and effort in designing the jigs was worth it – in the end they worked perfectly and the whole process was fairly trivial. A few swirls to flat out, but nothing major.

Final job on the sides was to reduce the plinth widths by 0.65mm:

Finished parts:

Filed the rounds on the webs:

Test assembled:

[Dr_GMJNParticipant @dr_gmjn]

A few questions:

1) The beds are slightly warped when tightened. I'd estimate perhaps 0.010" at a corner when the opposite corner is pushed down on a level surface. If I assemble with JB Weld on the cross-piece faces, then weight the sides down while nipping the screws up, presumably when the JB Weld has set, I can fully tighten the bolts (with Loctite retainer, and hopefully they would remain true, ready for the upper surface pads to be machined?

Any thoughts on this? Obviously if I can get away without skimming the lower surfaces, all the better because each one will need two setups to cover the length.

2) The end faces now need machining with their tapers. I think I'll use a spare 3 degree printed wedge for this:

The idea is to traverse the shell mill side to side, and feed down in increments. I'm not sure from the insert drawing whether it's designed to do this – i.e. with a 90 degree side faces. When I've tried it before on a test piece I seem to end up with scalloped face, as if the insert sides are tapered.

Any advice on this? Is it a matter of just incrementing in tiny amounts and flatting the resulting ridges?

3) Finally – the radiused internal corners. I know previous advice was to use JB Weld with a thickener. Having now used JB Weld, and finding it's a bit messy, is there any disadvantage to using white Milliput? I'm comfortable using it from plastic modelling experience, and I think I can sculpt it quite easily into radii with some basic tools and a damp cloth. Is Milliput robust enough for this application?

Thanks!

[JasonBModerator @jasonb]

It should work the way you describe as just gently weighting/clamping the parts will mean the JBW fills a very fine tapered gap and the screws will just keep everything in place. On the Victoria I did recently the base was twisted on the underside and bowed up in the middle of the top so had to shim with feeler gauges and then skim the bottom flat then remachine the top.

I've found the same whan machining a vertical face with teh insert cutters, you may be better off just using a 10 or 12mm cutter with 5mm high passes followed by a very shallow full height pass. Either stop 1mm high and us ethe insert cutter to form teh 0.8mm fillet or just cut right down and do the fillets at the end with filler.

I use Milliput quite a bit for internal fillets as it's easy to shape with a ball ended tool and wet paintbrush and there is almost no sanding. If you do go with JBW you may find it slumping to the bottom of all the vertical corners if you do plus there is then the filing and sanding to do a thickener or letting it sit for a while after mixing should see it stay where you put it. Car body filler is another alternative, better adhesion than Milliput and easier to sand than JBW,

Couple of items filleted with Superfine white.

Edited By JasonB on 15/05/2021 19:47:53

[Dr_GMJNParticipant @dr_gmjn]

Ok thanks Jason. I’ll use Milliput for the fillets.

I suppose the trick with JB Weld on the joints is to keep it off the screw threads so I can nip them up. I wonder if coating in Vaseline would do? I suppose no threadlock will be needed, since the counterbores will be full of JB Weld / Milliput eventually. Then again I could sequentially remove the screws after curing, then remove-fit with retainer?

What ball tool do you use for smoothing? Ball bearing stuck to a stick or something?

Ill try a 10mm end mill, and finish with the shell mill to get the same radius.

[JasonBModerator @jasonb]

You can stick a ball onto the end of a suitable handle or just round over the end of a rod. I tend to use these which are from my figure modeling days. Top one is used to apply a run of Milliput then dip the ball in water and draw along the corner. With luck you will get a nice fillet and two strips of waste material which are easily picked off and put back onto the pile. Wet artists paintbrush for a final clean up.

Yes some sort of release agent will allow then to be used to line things up but still turned when you need to tighten. I'm not keen on Milliput for filling over screw heads, usually opt for body filler, U-POL Easy was nice but now hard to get in smaller tins so have gone over to U-POL rapid but it lives up to it's name and is also a bit runnier so watch out.

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason – I'll get a set of those FWIW, they only seem to be a few quid off Amazon.

Assembled the beds with JB Weld on the mating faces as a liquid shim. At present everything is snug tight and lightly weighted down on a flat surface. Coated the screws in Vaseline, so hopefully once everything is set true and level I can remove each screw, and fully tighten with retainer:

Next chance I get to work on this will be Wednesday. Hopefully by then the JB Weld will be solid enough to put full load on.

[Dr_GMJNParticipant @dr_gmjn]

I got home earlier than expected today, so I spent a couple more hours on the beds. First off, remove and clean the screws, and replace with some retainer added:

There still appeared to be some residual twist in them, but a couple of passes over some abrasive paper on the granite slab got them perfect. I think the issue may have actually been a couple of small dings on the undersides. Still, the JB Weld gave a smooth finish to the joints, which will hopefully be invisible once painted.

Next up was to clamp to the printed wedge. I used a stop at the back to make sure it wouldn’t get pushed back with vibration:

Checked alignment to my mark-out:

Double-checked with a dial gauge on each end. It was within 0.004”, so good enough for this part:

Made about 10 Z passes with an end-mill, and incremented in X until I got to the line:

Finished the last couple of mm with the shell mill, which gave me the corner radius:

Still needs the plinth width reducing, which will get rid of the slight discontinuity, but so far so good:

Still another three to do, but enough for tonight.

[Dr_GMJNParticipant @dr_gmjn]

Continued with the remaining three end tapers this evening:

Then setup and trimmed the end plinth edges to match the sides:

I was happy with the result, with both bases ending up exactly the same overall outside and inside dimensions, and their top faces being within 0.004”:

…but when I put them back-to-back, the middle cross pieces didn’t quite match. There was about a 1.5mm discrepancy in the distance between them, side-to-side. Somewhat puzzled, I eventually checked the draw tapers, and found that on one base, both pieces had one vertical side, and one 3 degree side, instead of two 1.5 degree faces. The other base was fine:

As previously mentioned, getting the jigs right was confusing, so we must have ended up mixing the sides up when cutting the second faces.

So with heavy heart, I decided to dismantle the offending side, and re-make the two pieces. I assumed it would be next to impossible to separate them with the JB Weld and the Loctited screws (with their laughably soft caphead hexagons), but I was pretty shocked at how easily everything came undone:

So a bit of a setback, but some progress overall I think.

[JasonBModerator @jasonb]

You could enlarge the holes in the side plates slightly and just tilt the cross pieces.

You probably had some vaseline left in the holes which may have stopped the Loctite bonding.

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 20/05/2021 07:00:22:

You could enlarge the holes in the side plates slightly and just tilt the cross pieces.

You probably had some vaseline left in the holes which may have stopped the Loctite bonding.

I thought about enlarging the holes, but the counterbore diameters are a very close fit on the heads, so they'd have to be milled to a slight slot. The tops of the cross pieces are kind of flat in the middle too, so they'd also need correcting, and tilting them would give a gap at one side at the base.

I think overall it'll be quicker to make two new pieces, but be extra careful with orienting them on the wedges. It's very easy to get mixed up and confused with the sequence of machining to get equal angles each side. At least it is for me. Pure luck that both on the other bed were fine I suppose.

Re. the Loctite, I did thoroughly clean the holes with brake cleaner aerosol, and washed the screws, but I guess not enough. It wasn't like they were loose, but just didn't take much torque to undo them. I'll use araldite next time, and also the body filler should prevent them from loosening (not that they would).

[Dr_GMJNParticipant @dr_gmjn]

Re-made the two spacers. I know what went wrong, I think I got mixed up when swapping them on the 1.5/3 degree jigs, and ended up cancelling the taper on one side and doubling it on the other…

Full disclosure though – on one of them I turned the z-handwheel the wrong way, so that dig-in needed filling with JBWeld. I let that one go because a) it’ll be painted, and b) it’ll be pretty much invisible when the engine is assembled. At least it looks happy:

Also made a start on the mounting lugs which will be screwed into pockets milled into the bases:

Next job will be to drill the strips and radius the ends.

[Dr_GMJNParticipant @dr_gmjn]

So this is taking a lot longer than anticipated, but I’m wary of cutting corners. The whole thing sits on these beds so they have to be right despite looking pretty simple.

Anyway, drilled and countersunk the strips, and Made a start on milling their recesses. Marked out with verniers first, just as a sanity check for the DROs:

I needed the feet strips to fit precisely to a depth where the 0.8mm fillet in the plinth ended, that way I can replace it with Milliput, hopefully with seamless joints. So pocket depth and strip thickness needed to be identical:

Milling:

Drilling and tapping for the securing screws:

Finished:

Checking the fit:

Next job was to radius the ends of the feet. I wanted them precise, and identical, so the boy and I made some 13mm diameter steel filing rollers:

Worked great, so the feet were then split ready for fitting:

Final job today was to make the throttle bellcrank bosses out of aluminium:

They go in the pre-drilled holes in the bed sides, and will be pressed in with retainer, and then have a fillet of Milliput applied around the joint.

[Dr_GMJNParticipant @dr_gmjn]

Filled the counterbores with body filler and flatted back. They’ll probably need a bit more work before they’re invisible under a coat of paint:

Next job will be to fit the lugs.

[Dr_GMJNParticipant @dr_gmjn]

Fitted the lugs , they are a press-fit into their recesses, plus I applied some JB Weld to fill any residual gaps. The excess material on the inner faces will be filed and flatted back:

Also fitted the bellcrank bosses in a similar way:

They will have their faces milled back to within a couple of mm of the bed faces when I machine the top pads, then I'll apply a fillet of Milliput all around..

Question: When I'm machining the top surfaces to leave the cylinder, crosshead mount and main bearing pads, should I drill and tap the mounting holes as well? I want them to be in the centre of the pads, so I guess while the beds are clamped accurately to the mill table, it would be OK to do them at that stage? Only slight doubt is the cylinder feet holes, which will be positioned as set on JB Weld, and secured with a bolt. I wonder if I could somehow use the bed pads themselves as a jig for when I fix the cylinder to the feet? That would guarantee the feet are in the right position. My thinking is this would be done before any cylinder machining, ie the feet would have their bases machined and the mount holes drilled, then once set and bolted, the feet would be the datum for cylinder boring, and facing.

Or am I over-thinking this? Just seemed a good way of guaranteeing the cylinder and feet would be a perfect fit, and would also provide the first datum for boring.

Thanks.

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